Treatment of furnace gases to recover zinc oxide



.May 17, 1927.

J. F. CREGAN TREATMENT DE FRNAQE. GASES 'TOREGOAVER ZINC OXIDE filed Augflz. 1922 WMO 071m IN VEN TOR HSE/MHH? QNIUOGSM @qooof m Unio UE.

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Patented `May 17',l l927. y,

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.iomr r. camu, or PUEBLO, coLoaa-nqassmuoaro marcan Asummum AND mmm@ conm, or Nawfvxonx, N. Y., a coaroauxou or Nnwnsnsnm mmm or casas To ancovnngzmc oma.

Application August l2, 1922.l

It is well understood that the commercial value of zinc oxide depends to'ia consider-l able extent on the color of the pigment and physical texture. Discoloration results fromv Y a great variety of causes, and heretofor'efia high grade commercial product has ob; tained from zinc ores treatedinlarge qua-ntity in modern'types offurnace, Vsuch as vreverberatory furnaces, with diiiculty and:

lo only under favorable conditions.y

My process relates particularlyto 'a methy od of treating the metallic fumefrom ores that are smelted under high temperatures in open types of furnace, Such as reverberaf l5 tory furnaces, so as to produce a product having a uniform color and tint. 1 l .l The invention also relates to a method of recovering all of the zinc and'lead contained` rocess which in the ore by a continuous l 20 permits uninterrupted operation offallthe steps in the process from the charging of the* furnace to the recovery of the product.

Furthermore, the process' may be prac:

ticed under normal operating conditions'of a modern reverberatory furnace whereiniap= preciable variations of temperature are like-v ly to occur from time to time, and does not require a special form of furnace or any radical departure from standard practicewith respect to the smelting of the ores or the collection of the product.

In carrying out my invention, I propose to introduce a novel step in the treatment of zinc and lead fumes,( which consists` in subjecting the fumes to pronounced reduclng action under regulated temperature condi--y tions after the fume leaves the furnace but before it enters the usual combustion chamber.

This step in the process has the effect of producing a uniform or standardized product so that an reactions which subsequently occur in t e combustion chamber will have the same effect throughout the entire body vvoffume, and since these particular reactions Which occur in the combustion chamber are thoroughly understood, a uniform product of a pre-determined grade may be regularly obtained. y

This additional step in the process is preferably carried out in a special chamber or apparatus locatedv to receive the incoming fume from the furnace and to deliver the treated fume to a. combustion chamber, which may be alfwell-known construction land,.tiperated ccording to standard] practice.

referencelgzl p `ereduction chamber, is suppliedfwlth a-suitablereducing a nt, for example,gearbonemnoxide, in amp e quantity to reduceanfy'fume which may have be-.

burning of the zinc." If any additional heat l isfrequired, vit. v:may-.be suppliedl from fuel burners. communicating 4with the burning chamber. All of the zinc and lead in the slnelterA gases is completely reduced owing "tothe excess of reducing gas and the great heat2` and the metal fumes'passinto the coinl'b'ustlon chamber free yfrom the oxidation'in varying degree, which destroys the uniform color ofthe final. product. a"

In the accompanying .drawings I have c indicateddiagrammatically"a form of appa- .ratussuitablefor .'zarrying out my process,

inywhich,` 1 l c Fig. 1 indicatesajplan-view in section of one` form. of'l apparatus adapted for the purpose., l'

Fig. 2-jisa diagrammatic side elevation of the apparatus.'`

In the `apparatus shown diagrammatically in the drawings'tw`c y rA reverberatory furnaces A `of standardtypey and y#construction are shown.` The,;.c'har .maybe fed to these .furnacesinlanytdesired manner, but I prefer side feeding of thel charge` if the size and construction the furnace rmits. Both furnaces are connected throug suitable passages B w'itha reduction chamber C, which may be constructed of brick or other heatres1sting'material','and of suilcient capacity to hold. all of the gases produced by both of the reverberatories for a suiicient period of time during their passage therethrough for the necessary reductionto take place. The reduction chamber is also sup lied with a suitable reducing medium, suc as carbon monoxide, which' enters through the suppl pipe provided Vwith a control valve The outlet'from the reduction chamber may be controlledby a damper F, and communi- -The reduction chamber is Thiscliambc'rw hich for convenience ofbetween the carbonmon- 40 grade or state.

cates with` the usual combustion chamber G, and the flow regulated by the usual suction fan (not show/nf.

After the fume has been oxidized in the E combustion chamber, it passes to the baghouse or settling chamber H, of any wellknown construction.

In operation, the ores are smelted at the temperatures usually prevailing in reverberatory practice, for example from 2200 to 2400 degrees F. The greater part of the zinc and the lead passes off as metallic fume, but a considerable percentage may be oxidized, as it is dilicult to insure uniform re-v duction of all of the zinc and lead under the atmospheric conditions prevailing in a reverberatory furnace of modern construction. All of the fume passes with the other `gases into the reduction chamber, which is maintained at a temperature at or slightly below the temperature of the reverberatory furnace. This chamber, however, being supplied with a strongly reducing natural or artificial gas from an external source, ex-

ercises aI powerful reducing action on any fume which may have become oxidized in the reverberatory furnace, and causes all of the fume, includinglthat which has been only partly oxidizedas Well as the totally oxidized portion to be reduced to the metallic state.

Preferably the reduction chamber is of sufficient size to retain the fume for a period that will insure complete reduction, the rate of travel through the chamber being reg- 45 thecombustion chamber is 'under' complete control, a pigment of any desired commercial grade may be obtained.

By means of my improved process, all of the variable conditions of a reverberatory furnace which otherwise would deleteriously a'ect theqnality, grade, texture and coloration of the final product are entirely neutralized and overcome.` rlhe smelting operation whichnormally occurs in a reducing atmosphere owing` to the amount of fuel added to the charge, is in effect, by my process, transformed into a two-stage operation, wherein the smelting andthe reduction of the oxide are carried on in separate chambers or com- 60 artments, with but` a single charge of fuel.

ery little heat is lost in the operation, since the burning chamber may be placed contiguous to the furnace, or it may be separated therefrom a substantial distance. The

6; reducing conditions to which the fume is subjected are thus brought under exact and immediate control, therebyv assuring complete elimination of oxidized or partially oxidized particles and the delivery of a uniform product to the combustion chamber, wherein all of the factors which affect the product are likewise under control. Consequently the final product is a pigment of standard grade without coloration that is produced by a continuous process from the fume resulting from the smelting of the ores in a reverberatory furnace.

Having described my invent-ion, what I claim is l. ln the process which consists in smelting ores containing zinc, lead and other metals in a reverberatory furnace, the steps comprising removing the fumes into a separate chamber, and subjecting the fumes in said chamber to a reducing action while at a high temperature from the heat of the furnace. f

2. In the process of producing zinc oxides which consists in 4smelting ores containing zinc, lead and other metals in a reverberatory furnace, removing the metal fumes out of contact with the ores, and then subjecting the fumes to a reducing atmosphere by adding thereto an excess of reducing gas.

3. The process of forming zinc oxide, which consists in forming in a reverberatory furnace a zinc fume, subjecting said fume to a reducing atmosphere at a high temperature by adding thereto an excess of reducing gas, to reduce oxides formed during smelting, and then oxidizing the fume.

4r The proc-ess of oproducing zinc oxide, which consists in' smelting the charge in a reverberatory furnace, removing the fume from the furnace, subjecting the same to a reducing atmosphere without substantially lowering the temperature of the fume to completely reduce it, and then removing the fume and subjecting the same to an oxidizing atmosphere.

5. The process of producing zinc oxide, which consists in smelting zinc ores in a reverberatory furnace to produce a zinc fume, conducting said fume at a relatively high temperature to a separate chamber and mixing a Vreducing gas therewith in said chamber, and then oxidizing the metallic fume.

6. In the process of producing zinc oxide from zinc fume formed in a reverberatory furnace, the steps of oxidizing aad collecting the fume, which consist in removing the fume from the furnace and subjecting the same to reducing action thereby to completely reduce an oxide in the fume, oxidizing the fume in a separate chamber, and collecting the product.

"4. rIhe process of preparing zinc oxide from ores containing zinc which consists in smelting the ores in a reverberatory furifi-0 nace, removing the fume from' the presence of the ore and subjecting the same while'fat.

u hightemperature to the reducingaction of carbon monoxide gas to complete reduce the fume and then subjecting the umes to theaction of' a combustion chamber having an excess'of oxygen therein.v

8. The process of treating nevexjberatory v smelter gases containing zinc fume, which' vthe fume.

Signed at Pueblo, in the county of Pueblo l5 and State of Colorado, this" 24th day of July A. D. 1922. JOHN F. CREGAN. 

